CT apparatuses have increasing application in the field of medical diagnosis and other fields. A CT apparatus mainly comprises an X-ray source, a collimator, a detector, a data acquisition system (DAS) and a data processing system. The currently used arc-shaped detectors are relatively expensive. A spiral volumetric CT apparatus (SVCT) is a novel CT that uses a flat detector technology, in which a detector consists of several (e.g., 5) flat modules, greatly reducing the cost of the detector.
However, since there are gaps (i.e. physical gaps) between the plurality of flat modules in the flat detector, a band artifact (or closed to be a ring artifact) is generated in a reconstructed image, which reduces the quality of the reconstructed image and severely affects accuracy of medical diagnosis made based on the image. Therefore, when the image is reconstructed, there is a need for removing the band artifact in the image caused by the gaps in the detector.